Currently it has been found that calcium antagonists (Ca.sup.++ antagonists) which had been spotlighted as new agents for treating disorders of the cardiovascular system have a variety of pharmacological effects and are active not only against hypertension, angina pectoris, brain circulation and metabolism incompleteness and arrhythmia but also for prevention of arterial sclerosis and increase in effects of carcinostatic agents. Therefore indications as to the benefits of Ca.sup.++ antagonists continue to increase.
Ca.sup.++ antagonists which have been known include Nifedipine, Nicardipine, Verapamil, Diltiazem and the like. Up to this day, however, dihydropyrimidine derivatives have not often been investigated. Only a few references disclose said derivatives. (For example refer to Silversmith, E. F. J. Org. Chem., 27, 4090 (1962), Nasipuri, D. et al., Synthesis 1073 (1982), Kashima, C. Tetrahedron Letters 209 (1982) and Japanese Patent Public Disclosure No. 73572/59 (Bayer A.G.).) This can be considered to be due to the instability and tautomerism of the dihydropyrimidine derivatives.